We have been experiencing this weird issue with our 2000 series AP's.
Currently running firmware of 4.4 or 4.4.3 on our sectors and we've even tried using the new 4.5 but we receive the same problem regardless of the firmware.
Our SM's seem to disconnect from the AP for no valid reason and when I log in to check the system log on the AP, it reads INVALID SECURITY KEY. This would sometimes happen to a few SM's at a time or sometimes all of them on a certain AP.
Any help would be appreciated